Many conventional turbochargers include relatively massive cast center housings that include lubricant paths for bearing system lubrication and fluid coolant paths for heat extraction. The mass required to support these paths increases retention of heat by the housing and reduces the effectiveness of air flow as a means for cooling the housing. For example, the bearing portion of the housing (e.g., bore for receipt of a bearing or bearing system) is typically located centrally and interiorly and surrounded by material that forms the lubricant and fluid coolant paths. In such an example, air flow only passes by outer surfaces of the housing, which are at a distance from the bearing portion. Further, sand casting of interior coolant paths, especially for intricate paths, can complicate manufacture and raise quality control issues.
During operation, a turbine of a turbocharger is submitted to high gas temperatures; noting that temperatures are typically higher for gasoline engines compared to diesel engines. As a turbine housing transfers the exhaust heat to the center housing, the risk of bearing lubricant coking increases (e.g., consider oil as a lubricant). As mentioned, many conventional turbochargers rely, at least in part, on a fluid cooled center housing with embedded coolant paths. For types of turbochargers or applications that operate at lower temperatures, conventional center housings that rely solely on air and lubricant flow for cooling may suffice. Given lower temperature operation, the cost of fluid cooling in addition to air and lubricant cooling may not be justifiable.
In reality, operating temperatures of a turbocharger vary along a spectrum and can depend on many factors, which may vary during operation (e.g., demand, duration of operation, combustion conditions, external air temperature, temperature of lubricant or cooling fluid, etc.). Conventional approaches that categorize operation as “high temperature” or as “low temperature” and then select a high temperature turbocharger or a low temperature turbocharger depending on temperature category add significant costs. First, a decision must be made as to which category applies and, second, a turbocharger must be selected based on the category. For a given temperature spectrum, while the selected turbocharger may be a “good” fit, it may not be the optimal fit.
As described herein, various assemblies offer solutions to the existing conventional paradigm of “high” and “low” temperature turbochargers. In various examples, an assembly may include a center housing configured for lubricant and air flow cooling or optionally include a fluid jacket that provides, additionally, for fluid cooling. Other examples are also described.